The lead(II) coordination properties of the tetrapodal ligand DOTAM [1,4,7,10-tetrakis(carbamoylmethyl)-1,4,7,10-tetraaza-cyclododecane] have been investigated both in the solid state and in solution in order to ascertain the stereoactivity of the lone pair and to rationalize the structural effects of a cyclen-based scaffold on the metal uptake kinetics. The crystal structure of the free base shows that the pendant acetamide groups are not equivalent: two are folded over the macrocycle and maintained by an intramolecular hydrogen bond involving an amide hydrogen atom and a neighboring tertiary amine of the cyclen ring, while the other two are extended and point away from the macrocyclic cavity. The spontaneous reaction between Pb 2+ and DOTAM, even under mild acidic conditions, leads to a mononuclear complex. The crystal structure of [Pb(DOTAM)](NO 3 ) 2 ·3.5H 2 O reveals that the eight-coordinate metal cation is trapped inside the
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